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Hemoglobin – Blood Cells

Blood (Latin: sanguis, Greek: haima) is a suspension of cells in a saline solution containing protein. It makes up 6-8 % of the total body weight and has a pH value of 7.4. The blood carries out many essential functions and is the pivotal point of the whole organism. The following article provides, at a glance, the most important facts about this vital body fluid called blood.

00:01
Now, red cells are packed with haemoglobin.
Haemoglobin consists of four protein chainsand each of those carries a pocket for
a molecule called HAEM.
00:19
Now, these four protein chains vary slightly during
our development in embryonic, fetal timesYou have slightly different forms of haemoglobin.
but I'm not going to go into that todaybut in the adult, the 4 proteins consists of two alpha
chains and two beta chains as represented on the right.
00:41
and haem contains iron. Iron is critical
for the carriage of oxygen within haemoglobin.
00:51
In fact much of the iron within your body is
found within your haemoglobin.
00:55
We'll be discussing that later in the
lecture series.
01:01
and one thing we just need to consider is how
haemoglobin can take up and release oxygenand it releases oxygen to the tissues.
On the right you'll see a graph, it is calledan oxygen dissociation curve and on the x-axis,
we will see the partial pressure of oxygen,basically how much oxygen there is around.
And on the y-axis the percentage saturationof haemoglobin at that given partial pressure
of oxygen.
01:39
You'll see the dark green line
representing haemoglobin.
01:43
of course as the oxygen concentration goes up
the saturation goes up.
01:49
You can see it's not exactly a linear line, it is not
a straight line, it is what we call a sigmoid curve,it starts and then it accelerates.
That's because when one globin molecule binds oxygenit helps the others to bind, it's a cooperative
interaction and the haemoglobin can almost readilygrab the oxygen.
Another important point I want you to look aton that slide is the amount of saturation of
haemoglobin within arterial blood and venous blood.
02:24
So in the right you'll see the dotted line
showing arterial blood.
02:27
So it's a p02 of around 100 millimetres of mercury
which is what we see in arterial blood,haemoglobin is almost completely saturated whereas
if we look at blood coming back to the heart,venous blood, the partial pressure of oxygen is
around 40 millimetres of mercury and at that point,the haemoglobin is around 75% percent saturated.
It's around 25% of its capacity of oxygen carriagehas been lost as it's gone around the body.
There's still quite a lot of oxygen still remainingin venous blood even though when we take it
of course it looks very blue compared tored blood from arteries but there is excess
capacity to release more oxygen, perhaps ifthere is intense exercise. So we have some capacity
to increase oxygen delivery.
03:20
There are molecules within red cells such as
2-3-Diphosp hoglycerate which can shift this curveslightly to the left or the right so the body can
regulate how much oxygen it releases into the tissuesand we often find patients who have chronic anaemias
who have low levels of haemoglobin and red cellsthat their 2-3-DPG levels are such that they can
release more oxygen into the tissues to help theirbodies cope with metabolism.
Finally on that slide there is a dotted green-lineabove the haemoglobin curve and that is myoglobin
You can see there the myoglobin curve there'snot sigmoid and it has much more avidity for
oxygen than haemoglobin.
04:10
Haemoglobin needs to release oxygen into
the tissues.
04:17
Well it's not just about getting oxygen to tissues,
of course you know from your biochemistry lectureson respiration that carbon dioxide is formed and so
haemoglobin helps carbon dioxide to be transferredto the lungs and out of the body. So carbon dioxide
diffuses from tissues into red cells and there is anenzyme carbonic anhydrase which generates the
carbonic acid, that dissociates into bicarbonate ionand a proton. The protons are buffered by haemoglobin.
So haemoglobin has an important role in bufferingthe production of that acidic proton.
So as well as helping with oxygen delivery,haemoglobin helps with removal of carbon dioxide
from tissues.

About the Lecture

The lecture Hemoglobin – Blood Cells by Paul Moss, PhD is from the course Hematology: Basics.

Included Quiz Questions

Which one of these is NOT TRUE regarding adult haemoglobin (HbA)?

It holds on to oxygen very tightly compared to myoglobin.

It consists of 2 alpha and 2 beta chains.

Iron is a major constituent of haem.

It is not the major form of haemoglobin present at birth

Each globin chain carries a molecule of haem

Which of the following type of heme molecule does an adult have in the erythrocyte?

4 molecules, 2 alpha chains and 2 beta chains

4 molecules, 2 alpha chains and 2 gamma chains

4 molecules, 2 alpha chains and 2 delta chains

3molecules, 1 alpha chains and 2 beta chains

3 molecules, 2 alpha chains and 1 beta chains

Which of the following is FALSE regarding oxygen dissociation curve?

In the absence of 2,3-BPG, hemoglobin's affinity for oxygen decreases

Myoglobin is a hyperbolic shape in oxygen dissociation curve.

Hemoglobin A has a sigmoid shape in oxygen dissociation curve.

Increase in 2,3 DPG within the red cells can shift the red cell dissociation curve to the right.

When there is a left shift of the oxygen dissociation curve, there is a decrease in the 2,3 DPG.

What is the role of haemoglobin in carbon di oxide transport?

The protons generated are buffered by the haemoglobin.

Hemoglobin helps in the diffusion of carbon dioxide from tissue to the red cell.

Hemoglobin helps in generation of H2CO3.

Hemoglobin helps in dissociation of H2CO3 into HCO3+ and H+

Hemoglobin is not involved in the transport of CO2

Author of lecture Hemoglobin – Blood Cells

Paul Moss, PhD

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